HOT|COOL NO.3/2021 - "Don't waste it!"

HotCool is an international magazine on district heating and cooling. This edition is focusing on the worldwide issues with waste. One of the world's major environmental culprits is waste in landfills. Waste landfill leads to methane emissions, a greenhouse gas 30 times more harmful than CO2.

NO. 3 / 2021



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6 9 12 20 18




WASTE-TO-ENERGY By Henrik Søndergaard



HEAT AND HYDROGEN THE NEW POWER COUPLE By Hanne Kortegaard Støchkel and Jannick Buhl



DBDH Stæhr Johansens Vej 38 DK-2000 Frederiksberg Phone +45 8893 9150

Editor-in-Chief: Lars Gullev, VEKS

Total circulation: 8,000 copies in 60 countries 4 times per year

Design og medieproduktion Kailow A/S, CSR-, miljø- og arbejdsmiljøcertificeret.

Coordinating Editor: Linda Bertelsen, DBDH

ISSN 0904 9681

How can data help you deliver on the green agenda?

Heating and cooling account for 50% of Europe’s total energy consumption With the EU’s goal of improving energy efficiency with 32,5% by 2030, district heating utilities must produce, manage and distribute energy as efficiently as possible. The transparency created by smart metering solutions and frequent data is key to achieving this efficiency and deliver on the green agenda.


WHAT AWASTE! One of the world's major environmental culprits is waste in landfills. Waste landfill leads to methane emissions, a greenhouse gas 30 times more harmful than CO 2 .

Today, only 19% of all waste is recycled or composted, and only 11% is incinerated. The rest is sent to landfills (37%) or openly dumped (33%).

What a waste! Waste is a valuable resource when the organic content can be turned into biogas or incinerated for producing electricity and DH.

From the political debate, one could very well get the impression that waste incinera- tion is the greatest environmental sin of all. But that picture is misleading.

At a modern waste cogeneration plant, the energy in the non-recyclable waste is utilized while protecting the environment. Spreading the modern incineration method globally, hence waste not thrown in a landfill, will represent a global environmental and climate quantum leap. Talking about waste, Denmark is - with good reason - regarded as a small light in the dark, in an ocean of garbage. Particularly concerning utilizing the energy resource in the non-recyclable part of the waste, Denmark stands out to the rest of the world. Through waste incineration, Denmark has killed two climate birds with one stone. Denmark has removed landfills from the equation and can now, with new technology, capture CO 2 from waste incineration plants and use it as a resource for producing sustainable fuel. You can read all about it in this Hot Cool issue. DBDH publishes Hot Cool, but the main business is helping cities or regions in their green transition. We will help you find specific answers for a sustainable district heating solution or integrate green technology into an existing district heating system in your region – for free! Any city, or utility in the world, can call DBDH and find help for a green district heating solution suitable for their city. A similar system is often operating in Denmark, being the most advanced district heating country globally. DBDH then organizes visits to Danish reference utilities or expert delegations from Denmark to your city. For real or virtually in webinars or web meetings.

DBDH is a non-profit organization - so guidance by DBDH is free of charge. Just call us. We'd love to help you district energize your city!

Best regards

Lars Hummelmose, Managing Director, DBDH, +45 2990 0080

Carbon capture how it's done at ARC

By Nils Thor Rosted, Head of Communication, ARC

A new ground-breaking project can remove 500.000 tons of the CO 2 emitted fromAmager Ressource Center (ARC) annually from late 2025. This will serve as significant support for the Municipality of Copenhagen’s visionary ambition of becoming the world’s first CO 2 -neutral capital by 2025. Additionally, the project will innovate the capture process by reharvesting the residual heat from the process and turn it into district heating, thus lowering the overall costs of the process.

The incineration of the residual waste leads to unavoidable CO 2 emissions. The WtE sector can substantially contribute to decarbonizing the European economy by implementing CCS on WtE plants while creating green jobs and green growth. Pilot carbon capture at ARC The flue gas cleaning process at ARC is one of the best in the world. Almost all toxic flue gas components are being removed in the cleaning process. This means that nearly only steam and CO 2 are emitted into the atmosphere. ARC is determined to take the flue gas cleaning to the next level by implementing carbon capture. The goal is to capture 500.000 tons of the CO 2 emitted annually by late 2025.

Scientists agree that we need to reduce the amount of CO 2 in the atmosphere. This is possible when capturing and storing CO 2 . The IPCC, the European Commission, and the IEA consider deploying Carbon Capture and Storage (CCS) at a large scale as a crucial and necessary means to solving the climate crisis. CCS is vital to reaching the goal of the Paris Agreement to limit global warming below 2, preferably 1,5 degrees Celsius, compared to pre-industrial levels. One of the many tools to handle the climate crisis is reducing the total amount of waste produced. But as a society, we need to address the residual waste which cannot be reused or recycled. This is done in a good way at Waste-to-Energy (WtE) plants, where the residual waste is being turned into electricity and district heating. At ARC, we supply electricity for 80.000 households and district heating for 90.000 apartments.

On June 24th, Danish Minister for Climate, Energy, and Utilities,

ABOUT ARC Waste management is the core of ARC. Whether it’s recyclable or residual waste, our focus is on the environment and the climate. Every day of the year, we receive residual waste from households and companies in greater Copenhagen and supply heat and electricity in return. ARC manages 17 recycling stations, and every year close to a million customers hand in garden 'waste', used construction materials and other kinds of waste for recycling. Our goal is to make waste management climate-neutral and recycle as many materials as possible.

Five municipalities own ARC in the metropolitan Copenhagen area.

Explainer on how we capture CO 2 at ARC

Scan and view explainer on the carbon capture project at ARC

Ho w it works To capture CO 2 , the cleaned flue gas is led into a wet filter. When removing the CO 2 , the flue gas is led into a high tower (an absorber). The 40 degrees Celsius hot flue gas is moving towards the top of the tower while a liquid with alkaline amines is streaming down from above and is washing the CO 2 out of the flue gas. The amines are chemically binding the CO 2 molecules. The liquid with the absorbed CO 2 is lead to another high tower (a desorber). Here, the liquid is heated to 105 degrees Celsius to release the CO 2 molecules while the liquid with the alkaline amines goes back to the first tower and captures CO 2 again.

Dan Jørgensen and Lord Mayor of Copenhagen, Lars Weiss inaugurated a pilot unit for carbon capture at ARC.

The pilot unit is the first step towards carbon capture at ARC. It provides a unique opportunity to test the technology which can bring Denmark at the global forefront of carbon capture. During the 2nd half of 2021, ARC, DTU, Pentair, and Rambøll will be testing and maturing the technology, including the solvents used for capturing CO 2 . The goal is to optimize the capture technology to capture CO 2 most efficiently and cost- effectively.

Smoke without CO 2

This means that the liquid with alkaline amines can be reused.

The amine absorption technology is well known and has been used for decades. But it’s always been very energy-intensive and expensive. The project at ARC aims to reduce energy consumption and overall cost level by optimizing the energy flows inside the carbon capture unit, reharvesting the residual heat from the capture process, and using it for district heating. Carbon capturewithnet zero energy consumption ARC is producing electricity, some of which can be used for the carbon

Captured CO 2

Alkaline amines

Fluegas with CO 2

Captured CO 2



District heating

Carbon capture with net zero energy consumption.

FACTS • The pilot unit for carbon capture is co-funded by the partners ARC, DTU, Pentair and Rambøll. The partners represent a large emitter (ARC), the most skilled scientists within carbon capture (DTU), a manufacturer of carbon capture units with a proven track record (Pentair) and consulting engineers with expert insights into waste-to-energy, district heating and carbon capture (Ramboll). • The project is being co-funded (DKK 30 mio.) by the Energy Technology Development and Demonstration Program (EUDP). • The pilot unit can capture up to 850 kg. CO 2 / day and will be operational throughout 2021.

 Explainer on the carbon capture project at ARC

Scan and view how we capture CO2 at ARC

On June 24 th , Danish Minister for Climate, Energy, and Utilities, Dan Jørgensen and Lord Mayor of Copenhagen, Lars Weiss inaugurated a pilot unit for carbon capture at ARC.

The way to reach net-zero energy consumption is to study the energy streams of the capture unit.

capture unit. The residual heat from the capture process is being turned into district heating.

“We need to be certain that the amine liquid entering the absorber tower is cold enough. When it comes from the desorber, it will run through a heat exchanger, but the temperature of the amine won’t be low enough. In standard

“In terms of megawatts, the capture process is energy neutral. But in terms of economy, there is a loss since electricity has a higher economic value than district heating”, says ARC program manager Peter Blinksbjerg.

to the flue gas. These chemical agents need to be cleaned in a separate cleaning process”, says Peter Blinksbjerg and adds:

installations, you would either dry cool it or take in seawater to cool it. But instead, we will harvest the residual heat with heat pumps and send it into the district heating network”, says Peter Blinksbjerg and continues: “The amine liquid with the absorbed CO 2 will release the CO 2 molecules when it is heated to 105 degrees Celsius. This heating process releases huge amounts of water vapor which holds much energy. It takes a lot of energy to evaporate it, and it releases a lot of energy when it’s being liquified by cooling. So, when liquifying the CO 2 before cooling it, you gain a lot of condensation heat from the water vapor, which we can harvest and make use of”. This is why a district heating network is of great importance when bringing down costs of carbon capture. The traditional energy loss from the capture process can be turned into a source of income. Increased demands for flue gas cleaning The traditional setup of a carbon capture unit is – basically speaking – an absorber and a desorber. At ARC, we’ve added two additional towers, one of which supports the goal of net- zero energy consumption while the other is added to cleanse the flue gas after the carbon capture process. “When the flue gas is led through the absorber, it is mixed with the amine liquid through a large surface area. But when the amine liquid captures the CO 2 , we cannot avoid that there can be other chemical agents that will go from the amine liquid

“When implementing carbon capture, we don’t want to introduce a potential new source of air pollution. Therefore, the fourth tower of the pilot capture unit is sort of a washing section with several possible ways of cleaning the flue gas with both water, alkaline liquid, etc.”. The steps ahead – and necessary preconditions The pilot carbon capture unit at ARC is capturing app. 850 kg. of CO 2 /day. It is a stepping stone towards a scaled-up demonstration unit planned to be operational in early 2023. The demonstration unit will capture 12 tons of CO 2 /day. By late 2025 the full-scale carbon capture unit will be operational, capturing 500.000 tons of CO 2 /year. To meet this ambitious time schedule, the right policies and economic incentives must be set up by the Danish Parliament very soon. Furthermore, full-scale carbon capture at ARC – as well as on any other plant – is dependent on the existence of a mature value chain. This means that both transportation (by pipeline and/or ship) and storage facilities (offshore or nearshore) must be available at competitive prices.

For further information please contact: Nils Thor Rosted,

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Waste-to-Energy A Solution for the World’s 2-Billion-Ton Trash Problem

At a modern waste cogeneration plant, the energy in the non-recyclable waste is utilized while protecting the environment. Spreading the modern incineration method globally, hence waste not thrown in a landfill, will represent a global environmental and climate quantum leap.

By Henrik Søndergaard, editor at DBDH

of all plastic waste ever produced HAS BEEN RECYCLED 9%



of all plastic waste is sent to LANDFILLS, DUMPS OR IN NATURAL ENVIRONMENT

of all plastic waste has been INCINERATED

through controlled composting of organic waste, expanded sanitation coverage, and state-of-the-art incineration.

Today, merely 19% of all waste is recycled or composted, while 11% is incinerated. The rest is sent to landfills (37%) or openly dumped 33%). According to the Intergovernmental Panel on Climate Change - IPPC Waste Management report, waste is a con- tributor to global greenhouse gas (GHG) emissions. The larg- est source is landfill methane (CH4), followed by wastewater CH4 and nitrous oxide (N2O). Minor emissions of carbon diox- ide (CO 2 ) result from the incineration of waste containing fossil carbon (C) (plastics; synthetic textiles).

Incineration and industrial co-combustion for Waste-to- Energy (WtE) provide significant renewable energy benefits and fossil fuel offsets. Currently, >130 million tonnes of waste per year are incinerated at over 600 plants. Thermal process- es with advanced emission controls are proven technology but more costly than controlled landfilling with landfill gas recovery; however, thermal processes become more viable as energy prices increase. The total global economic mitigation potential for reducing landfill CH4 emissions in 2030 is estimated to be >1000 MtCO 2 - eq (or 70% of estimated emissions) at costs below 100 US$/ tCO 2 -eq/yr. • 20–30% of projected emissions for 2030 can be reduced at negative cost • 30–50% at costs <20 US$/tCO 2 -eq/yr. • More significant emission reductions are achievable at higher costs, with most of the additional mitigationpotential coming from thermal processes for WtE. Waste is a resource for green energy. Waste is a valuable re- source for organic content turned into biogas or inciner- ated for producing electricity and district heating (DH).

Landfill is the worst of all solutions – and by far the most popu- lar!

Landfill gas (LFG) is a natural byproduct of the decomposition of organic material in landfills. LFG is composed of roughly 50 percent methane (the primary component of natural gas), 50 percent carbon dioxide (CO 2 ), and a small amount of non- methane organic compounds. Methane is a potent green- house gas 28 to 36 times more effective than CO 2 at trapping heat in the atmosphere over 100 years, per the latest IPCC as- sessment report (AR5) Existing waste-management practices can provide effective mitigation of GHG emissions from this sector: a wide range of mature, environmentally effective technologies are available to mitigate emissions and provide public health, environmental protection, and sustainable development co-benefits. These technologies can directly reduce GHG emissions through landfill gas recovery, improved landfill practices, engineered wastewater management, or avoid significant GHG generation

See here how one of the best Waste-to-Energy plants in the World operates:

Copenhill - How the plant works

7. SMOKE PURIFICATION Each furnace line has a separate smoke treatment plant consisting of an electric filter, a catalytic converter, three scrubbers and a dust filter. In the electric filter, most of the dust is removed. The smoke is then passed through the catalyst, which removes NOx. The first scrub removes hydrochloric acid, mercury and other undesirable substances. The second scrub removes SO2 using lime.

6. SLAG AND FLY ASH When the waste is burned, 17-20% is left as slag by weight. The slag consists of ash from the waste, gravel, sand, metals and other materials that cannot burn. In a sorting plant the slag is reversed and watered for 3-4 months, in a process called maturation. The purpose of the process is to get particles from heavy metals to bind to the slag particles so that they cannot be washed out. After maturation, metals are sorted out for recycling - for every 200 kg slag can be sorted out 10-15 kg metal, which can be reused. The slag is then harped so that it has the same characteristic as stable gravel and can be used for replenishment for construction works. The fly ash and other by-products of the smoke purification are used as a substitute for lime to neutralize residues from other industries. The mixture is cemented and used to recreate the landscape of a disused limestone quarry.





The entire energy plant is running 24 hours a day, 365 days a year. To monitor the process from weigh-in to water treatment, the facility is staffed 24 hours a day. Through a Control, Regulation and Monitoring System (SCADA-system), which contains approximately 10,000 alarm points and visual systems, control room employees monitor the entire process. Amager Bakke has 850 pumps, fans and compres- sors, 1,800 valves and 3,300 measuring instruments.



Waste contains a lot of water - most of the water is collected in the smoke purification, so at full load on the two furnaces, up to 13 m3/h of wastewater – pH between 0.5 and 2.5 - is produced. Purification and neutralization of water takes place in four steps: STEP 1: In the first cleaning step, add lime and lye, which neutralizes the wastewater to a pH of between 7 and 8. STEP 2: Particles are precipitated in the water like sludge in large tanks. The wet sludge is passed on to a filter press, where most water is squeezed out. The sludge is collected in a container and deposited together with the fly ash. STEP 3: The water is passed through some sand filters and ammonia strippers. Here, the smaller particles that were not previously precipitated are filtered out. The excess ammonia in the ammonia strips is recycled for smoke purifier. STEP 4: Carbon filters and ion exchange. Here, the water is cleaned of the last remnants of organic materials and metals.

The third scrubber is a so-called condensing scrub - here water vapor is condensed into water droplets, so that heat pumps can take advantage of residual heat in the smoke. The residual heat is sent via heat exchangers into the DH network. In total, about 20% of DH production comes from the heat pumps, which are connected to the smoke purifi- cation. The last cleaning step is a wet dust filter, which removes the last remnants of dust in the smoke. Before the purified smoke enters the chimney, it passes a measuring station, which constantly records the levels of contaminants. Copenhill’s chimney is 123 meters high. It contains three separate chimney pipes: one for each of the two furnace lines, and one for an emergency power generator.

4. THE BOILERS Copenhill has two boilers - each can produce up to 137 tons of steam pr. hour. The ovens are built together with their own boiler, so that the hot smoke from the oven rises up and transfers its energy directly to the water in the pipes. The steam has a pressure of 69 bar and temp. of 440OC. Steam from both boilers is collected in a common steam pipe, called steam rail, from which the steam is passed on to the steam turbine. In order for both ovens and boilers to expand when they get hot, they are not on the floor, but are instead hung up in the steel structure, in the ceiling. 90% of the energy in the waste is converted into high-pressure steam.

3. THE OVEN SYSTEM Copenhill’s two identical incinerators each have a capacity of 25-35 tons of waste per hour. When the waste is filled into the in-the-firing tunnel, it falls through the waste shaft. Here it forms an airtight stopper, so that there is always pressure in the oven. As the waste moves forward, it gradually ignites. It takes 1.5-2 hours to burn the waste in the oven at a temperature of 950-1,100OC. The temperature is controlled by blowing air through the holes in the grates. Once the waste has come to the end of the grate, virtually all energy is released like hot smoke. For each ton of waste, Copenhill can produce 2.7 MWh of district heating (DH) and 0.8 MWh of power.

1. WASTE ARRIVES Receives residual waste from approxi- mately 600,000 citizens and 68,000 businesses. There are 250-300 lorries with waste to be weighed and recorded every day. It is investigated whether the waste has been sorted properly and that it does not contain elements that could damage the plant or that are toxic.







Waste is tipped directly into the silo, which is 30x50 meters and has a total height of 36 meters. The silo can hold about 22,000 tons of waste - that equates to about three weeks of waste. Two automatic grabs - each can lift up to 15 tons of waste - make sure to mix the waste so that it becomes fairly uniform. The homogeneity of the waste is important for the combustion process to be as stable as possible. To reduce odors from the waste, there is negative pressure in the unloading hall. The air that is sucked out of the hall is used in the ovens.

5. TURBINE AND HEAT EXCHANGER A steam turbine is connected to a generator, which converts the steam energy into electricity. Electricity production is up to 63 MW. Once the turbine has taken the pressure and heat off the steam, heat energy remains. This energy is used in the district heating (DH) exchangers. In the heat exchangers, DH water is heated, which is sent into the DH system. DH production is up to 247 MW. At Copenhill, the production of electricity and DH is flexible: If market price for electricity is high, all the steam is passed through the turbine. If, on the other hand, there is a need for a lot of DH, the steam is diverted around the turbine (by-pass) and directly into the heat exchangers.

For further information please contact: Henrik Søndergaard,


5 th


By Oddgeir Gudmundsson and Jan Eric Thorsen, Danfoss Climate Solution, Denmark.

In recent years, the 5 th generation of DH has been emerging. But what are the drivers behind the development, and how is it positioned compared to the prior generations? Before a meaningful answer, one needs to know how the 5 th generation's definition deviates from the definition of the 4 th generation and what impact the difference has on the supply system.

“The fifth generation” In recent years, the fifth generation of DH has been emerg- ing. But what are the drivers behind the development, and how is it positioned compared to the prior generations? Be- fore a meaningful answer, one needs to know how the fifth generation's definition deviates from the definition of the 4 th generation and what impact the difference has on the supply system. To answer this, one needs to know what the original idea was behind the definition of the 4 th generation. This can be read out of the generation figure, Figure 1, which shows the transi- tion from fossil fuels to a renewable energy source; it further shows an intelligent integrated energy system where the heating sector is coupled with the power, industry, and cool- ing sectors. It is about energy efficiency, it is about sustainabil- ity, and it is about demand-driven energy systems. When looking into the main ideas behind the 5 th generation, one quickly finds that it is identical to the 4 th generation. It is about energy efficiency, sustainability, and demand-driven thermal supply. The difference between the generations does not lie in the purpose of the system but in how the systems are designed to fulfill their purpose.

District heating (DH) is here to stay. Looking back on the history of DH, it goes quite some years back. During the years, it has developed to fulfill the demands as they came up, typically driven by the need for reduced investment and heat costs, low- er equipment space demands, concerns of energy efficiency, environment, longer lifetime, and lower fire risks. In 2014 an article [1] was published that categorized the historical devel- opment into four generations. Each generation was defined by significant changes in the technology or purpose compared to the prior generation. Currently, most DH schemes being operated are categorized as being at the 3 rd generation DH technology stage and starting its transition to the 4 th genera- tion. The transition is driven by the challenge of the future non-fossil and renewable-based energy system. At the same time, there is active work being performed in the research community to see how this great technology can be innovated even further. This has led to the concept of an ambient temperature distri- bution grid, commonly called the 5 th generation DH. Each end- user operates his heat pump to adapt the supply temperature to his own needs. The research has mainly been focused on case studies and few small-scale concept validation projects. What has generally been missing is a direct comparison of the 5th generation to the 4 th generation. What are the differences between the generations that impact the integration potential of the energy supply system? This article tries to address that.

Before digging into the differences, we need to define what energy sources and heat plants mean:

Concept of 4 th Generation DH in comparison to the previous three generations. 4DH




4G: 4th GENERATION Low energy demands Smart energy (optimum

Steam system, steampipes in concrete ducts

Pressurised hot-water system Heavy equipment Large ”build on site”stations

Pre-insulated pipes Industrialised compact substations (also with insulation) Metering and monitoring

interaction of energy sources, distribution and consumption) 2-way DH

< 200 °C

DH flow

> 100 °C

< 100 °C

DH return

50-60 °C (70 °C) ~ 25 °C (ULTDH <50 °C)

< 80 °C

< 70 °C

< 45 °C


Data center

Future energy source

Seasonal heat storage

Large scale solar

Biomass conversion

Large scale solar

2-way District Heating e.g. supermarket

Biomass CHP Biomass


PV, Wave Wind surplus Electricity

CHP biomass

Industry surplus

Cold storage

Centralised district cooling plant

Heat storage

Heat storage

Heat storage

CHP waste CHP coal CHP oil

Centralised heat pump

CHP coal CHP oil

Steam storage

Industry surplus

Also low energy buildings

Coal Waste

Gas, Waste Oil, Coal

Coal Waste

CHPwaste incineration

Local District Heating

District Heating

District Heating

District Heating

Development (District Heating generation) / Period of best available technology

1G / 1880-1930

3G / 1980-2020

4G / 2020-2050

2G / 1930-1980

Figure 1: Illustration of the concept of 4 th Generation DH in comparison to the previous three generations.

Energy source: Energy source is the primary energy input to the system. It can be any energy source prior to the conversion to the desired energy form. In the case of a building, thermal demands are heat at an immediately functional temperature level.

that the losers are neither the end-users nor the society.

As the saying goes: You lose some, and you win some. The winnings from having no distribution loss are that no heat is lost between the heat source and the end-users, and there is no need for insulation. Having no insulation further means a cheaper distribution system (at least in theory). Potential loss- es from having “no losses” could, on the other hand, be lost opportunities and secondary inefficiencies. As lost opportunities can be too many to count, one should focus on those who are likely to be most important, such as: • Ability to use alternative energy sources capable of gener- ating heat at immediately useful temperature levels, such as waste heat from industry, power production, or any oth- er new types of energy sources that may be discovered in the local area - Operating uninsulated pipe network at higher than the ambient temperature would lead to significant distribu- tion losses • Ability to use more energy and cost-efficient large-scale centralized heat plants • Avoidance of upgrading or specifying unnecessarily strong power distribution grid - As thermal demand is a vast majority of building energy demands, there is a high risk that the heating demand in an individualized electrified heating system would be defining the power connection capacities • Ability to have long-term decoupling of the thermal de- mand and thermal generation - Long-term decoupling can only be achieved via central thermal storage capable of fulfilling thermal demands at immediately functional temperature levels 5G claim: Uninsulated pipe network is cheaper While saving investment costs by using uninsulated pipe is certainly an interesting point. It also deserves a closer look: One needs to consider the system design conditions, par- ticularly the expected temperature difference between the supply and return flow, as this will define the required pipe diameters of the distribution network. In that respect, two main factors can negatively influence the design of ambient loop systems. • The ambient temperature heat sources tend to cool down during the heating season. • The higher the heat pump efficiency, the smaller the tem- perature difference is across the evaporator, e.g., the cool- ing of the heat source. Both points lead to squeezing the system temperature difference and lead to the need for large pipe dimensions. In the perspective of potential cooling demands being used for regenerating the heat supply in the 5G system it should be considered that during the heating season the likelihood of

Heat plant: Heat plant is the conversion technology used to convert the energy source to the desired temperature level.

With these definitions in place, we can make a clear distinc- tion between the 4 th generation and the 5 th generation: • The 4 th and 1 st to 3 rd generations rely on centralized heat plants to convert the energy source to heat at immediately useful temperature levels for the end-user. • The 5 th generation is taking a different approach, which is to deliver the energy source to the end-user, which uses his heat plant to convert that energy source to heat at an immediately useful temperature level. For the 4 th generation, the form/type of the applied primary energy source and central heat plants are not restricted. For the 5 th generation, the primary energy source is low-quality heat at too low levels for direct utilization, mainly ambient heat sources, and the heating plant is a building level / end- user heat pump. This individualization of the temperature upgrading of am- bient sources provides the fundamental difference between the 5 th generation and the prior generations. It provides the platform to compare the 5 th generation to the 4 th generation. From a technical point of view, the moving of the heating plant from a central location towards the end-user has some benefits, for example: • Distribution heat losses may become insignificant, even irrelevant, as no energy has been spent on upgrading the input energy, ambient heat, to useful temperature levels. • With no distribution losses, pipe insulation becomes irrel- evant, which in theory will lead to a cheaper distribution network. • The heat plants (end-user heat pumps) can be adapted to the temperature requirement of each end-user, in theory leading to better heat generation efficiency. • Possibility to integrate cooling into the same system by enabling the end-user heat pumps to operate in a cooling mode and deliver the waste heat into the distribution grid. From the outset, these are quite promising benefits, at least at first glance. Since everything is subjected to local conditions, and even from the viewer's standpoint, it is perhaps a good idea to look into these benefits from a broader perspective. 5G claim: No distribution loss is the best First, nobody likes losses, except for parents losing games to their happy and smiling kids (which is technically a win in the bigger picture). Now, if no one likes losses, why should we bother with a closer look at the lossless distribution? If there are winners, there are also losers. We just need to make sure

Pipe dimensions for capacities below 2,000 kW

Pipe dimensions for capacities above 2,000 kW

Figure 2: Impact of the temperature difference on the pipe dimension for a given heat transfer capacity.

we have an additional parameter at play. For dimensions below DN 200, the insulated pipe system can be optimized by incorporating both the supply and the return pipe into the same sleeve, e.g., Twin pipes. The twin-pipe concept has the benefit of reducing the trench requirement compared to two single pipes; see the right side of Figure 3. Additionally, twin pipes significantly reduce heat losses from the distribu- tion pipe network compared to a set of single pipes. This boils down to the following fact: The generally larger pipe dimen- sions required for the 5 th generation and the availability of the Twin pipe concept for the 4th generation reduce the cost-ben- efit of an uninsulated pipe network.

any user operating in a cooling mode is particularly low. The lack of regeneration from cooling leads to the pipe network being dimensioned like traditional district heating systems, from the heat source towards the end-users. The impact of the temperature difference on the required pipe size for capacities of few kilowatts to 10 megawatts is shown in Figure 2. Not particularly surprisingly, the figure shows that the lower the temperature difference, the larger the required pipe dimension is. This is important as the pipe dimension has a direct impact on the trenching cost of the network. The bigger the pipe, the bigger the trench. Secondly, the bigger the pipe is, the more costly it becomes.

All in all, these factors can effectively neutralize the cost-benefit of applying an uninsulated pipe network.

When comparing the 5 th generation with the 4 th generation,

Two single uninsulated pipes in a trench

Twin pipe in a trench

Figure 3: Trenches of uninsulated pipes, left, and twin pipes, right.

5G claim: End-user heat generation leads to higher efficiencies This is a fascinating point. Without a doubt, the efficiency of heat pumps is higher the lower the temperature lift, i.e., the less you need to increase the supply temperature, the more efficient your operation becomes.

a. In principle the savings of losses in the power grid can go long way towards the heat loss in the 4 th generation dis- trict heating system, considering the COP of the central- ized heat pump 5. Centralized heat pumps can access power at lower cost due to the aggregated demand and by connecting with the high voltage grid 6. In a combination with a district cooling system both sides of the heat pump can be exploited, creating a uniquely high system energy efficiency a. While this is commonly mentioned as inherent part of the 5G systems its is not to the same extent, as waste heat from the cooling operation in 5G systems is not delivered at a useful temperature level to the loop, it is mainly tak- ing over part of the loop regeneration purposes of the heat source 7. Centralized heat pumps and centralized thermal storages are uniquely positioned to decouple the heat/cool demand and the heat/cool generation, enabling it to take greater ad- vantage of electricity tariffs, low carbon power periods and provide power grid balancing services

There is, however, more at stake here than one might initially consider. For example:

1. Centralized heat generation enables economy of scale by taking advantages of simultaneities and the aggregation of the heat demand

2. Large scale centralized heat pumps are both more cost and energy efficient than small end-user heat pumps

3. Large scale centralized heat pumps are professionally main- tained and the operation is optimized, leading to stable and energy efficient operation and long lifetimes 4. Centralized heat pumps connect to a higher voltage grid, which avoids potential power losses in the power transfor- mation stations and distribution grid

Comparison of the solutions – Annual cost of heat for the average connected building in Copenhagen

Figure 4: Levelized cost of heating for high energy (HE) and low energy (LE) buildings in Copenhagen for various thermal source temperatures. ATDH is the 5 th generation and LTDH is the 4 th generation.

The above points translate to better cost optimization of the heat generation.

buildings. Finally, the case analysis considered the impact the thermal source's temperature would have on the economics of the system. The results of the case analysis are shown in Figures 4 and 5. The figures clearly show that 4 th generation district heating systems have significantly better economics than 5 th generation systems. Final words As the case study focused on a suburban setting, which is typically considered outside of the core district heating zones, which are densely populated inner cities with concentrated heating demands, it points to that the 5th generation requires specific conditions to be in place to ensure its competitiveness. These conditions are like to occur when an economy of scale from central heat generation is not achievable. These condi- tions might occur at small settlements with relatively few houses. Instead of each house operating their own ambient heat source, for example a geothermal loop, the settlement could share a larger and more cost-efficient geothermal loop. In that sense the 5th generation can also be classified as ex- tended individual heat pump system.

But there is also the fact that if there is an insulated network, the system is significantly better positioned to enable energy- efficient utilization of any heat source with a higher tempera- ture level than the ambient. In ambient loops, higher waste heat temperatures than the ambient could only be used with high heat losses in the uninsulated network. 5G claim: Cooling is an integral part of the 5G solution and effectively separates 5G from 4G This is the only part where the 5 th generation has a clear ad- vantage over the 4 th generation regarding residential cooling demands, at least compared to the original definition of the 4 th generation, which was written by Scandinavians, where resi- dential cooling demand is virtually non-existing. In principle, the cooling demand could be integrated into the 4 th generation the same way as in the 5 th generation, by us- ing the distribution network as a heat sink for end-user located heat pumps. For commercial cooling demands, which tend to be con- centrated and more prominent than residential cooling de- mands, the most efficient supply systemwould be a dedicated district coolingsystem, as is applied inParis, Stockholm, Helsinki, Copenhagen and many more cities around the world. How does the 5 th generation economically stack up to the 4 th generation? Due to the relatively few 5 th generation systems, there is a gen- eral lack of economic comparison of these solutions. This has, however, been compared in the paper “Economic compari- son of 4GDH and 5GDH systems – Using a case study” [2]. The case analysis compared the cost of these two generations sup- plying a suburb area in two locations with different climates, Copenhagen and London. The case analysis further investigat- ed the impact on the system economics if it would be supply- ing either existing high energy buildings or new low energy


Lund, H. et. al. , 4 th Generation District Heating (4GDH). Integrating Smart Thermal Grids into Future Sustainable Energy Systems. Energy, vol. 68, 1-11, 2014.

Gudmundsson, O. et. al. , Economic comparison of 4GDH and 5GDH systems – Using a case study. Energy, vol. 238, 2021. 2021.121613

For further information please contact: Oddgeir Gudmundsson,

Comparison of the solutions – Annual cost of heat for the average connected building in London

Figure 5: Levelized cost of heating for high energy (HE) and low energy (LE) buildings in London for various thermal source temperatures. ATDH is the 5 th generation and LTDH is the 4 th generation.

Heat and hydrogen THE NEWPOWER COUPLE A key to making Power-to-Xmuch more energy-efficient - and cost-effective - is district heating (DH). A key to making 100% carbon neutral DH is integrating excess heat from other sectors. Also, municipalities and governments are beginning to see that, together, heat and hydrogen can increase the speed and quality of the green transition.

Don't use hydrogen for heating. Use DH and PtX in combination.

By Hanne Kortegaard Støchkel, author of the report, Project Development Manager, DBDH Jannick Buhl, Chefkonsulent, Dansk Fjernvarme

Report on integration of Power-to-X and district heating This article is based on a comprehensive report on the integra- tion of Power-to-X (PtX) and district heating (DH) in Denmark. The report is published by the Danish District Heating Associa- tion, the think tank Grøn Energi, COWI and TVIS. Why Hydrogen? PtX is closely tied to the green transition in the transport of goods by road, sea, and air and the production of carbon-neu- tral fertilizers for agriculture and carbon-neutral forms of prod- ucts such as steel, plastic, and chemical products. This gives a rapidly increasing demand for green hydrogen in the coming year. This underlines the need to use green hydrogen where it is most needed and most valuable – and that is not for heat- ing. For heating, much better alternatives exist already today. In rural areas, this could be small, electric heat pumps. In more densely populated areas, the cheapest and most efficient solu- tion is DH based on renewable heat source and reused surplus heat. Some argue that hydrogen should be used in households for heating, but it makes much more sense to combine PtX with DH and use the surplus from the hydrogen production for heating. PtX processes involve energy losses in the form of heat, and infrastructure is needed to collect and use that heat. That is where DH systems come in (Figure 1).

requires two things: green hydrogen and green carbon. The hy- drogen comes from electrolysis. Carbon, in the form of concen- trated, green CO 2 , will become a challenge, but both WtE and biomass-based units for heat production are essential sites for collecting large quantities of CO 2 for storage or use in e-fuels. Don’t waste green energy The forecasted electricity consumption for PtX is significant and so are the accompanying energy losses. Assessments on electrolysis show that usable waste heat makes up around 10- 25 % of the energy input to the hydrogen plant. With energy ef- ficiency becoming more and more important, energy losses on that scale must be investigated and converted into solutions. Faster and better green transition Due to the climate challenges, we have to develop efficient so- lutions and implement them quickly. But risks and creating a good business case for hydrogen production are holding back PtX. By integrating PtX and DH, the owner of the hydrogen plant can sell the surplus heat to the DH company - generat- ing revenue and increasing the competitiveness. From the DH point of view, utilizing surplus heat fromhydrogen production can replace fossil-based heat production and pro- vide energy for new DH areas currently heated by natural gas.

A less known link between PtX and DH comes through the waste-to-energy (WtE) plants. The production of most e-fuels



PtX refers to green power to produce a product (X), which could be green hydrogen, basic green chemicals, e-methane, e-methanol, green ammonia, or green aviation fuel. All PtX processes require hydrogen. Electrolysis is, therefore, an essential element in the green transition because it converts water into hydrogen and oxygen using green electricity.

Energy loss (heat)

District heating

Figure 1: PtX converts power into another energy source called 'X,' for instance, hydrogen, methanol, or aviation fuel. In energy conversions, a substantial part of the energy is converted into surplus heat - potentially to be utilized for DH.


Process heat Businesses

surplus heat


Direct utilization of waste heat is difficult


Process heat Businesses

surplus heat

District heating

Revenue from district heating Extra hydrogen revenue Original hydrogen revenue

Utilization of waste heat

Green district heating replace fossil-based process heat

Figure 2: Revenue for 20 MW electrolysis plant with a DH connection. In the report, the surplus heat at (70° C) is valued at 27 EUR/MWh during the winter and 20 EUR/MWh during the summer, whereas the surplus heat at 35° C is valued at 2 EUR/MWh in the analyses. The additional hydrogen revenue results from extra operating hours due to the DH revenue. Assumptions are described in the report.

Figure 3: The business sector needs green alternatives to replace fossil process heat. The report explains why surplus heat from PtX needs access to a DH system. Direct utilization for industrial processes and heating is difficult (top), whereas the integration can be made possible with district heating (bottom).

PtX plants require planning and cooperation, and potential use of surplus heat should be included as early as possible in the process. Improving the business case for green hydrogen The surplus heat from hydrogen production can contribute to the business case of electrolysis. If connected to a DH sys- tem, the heat has value and can be sold to generate revenue. The electricity price primarily sets The number of operating hours for the hydrogen plant is primarily set by the electricity price. Therefore, the revenue from the surplus heat is the ad- ditional effect of increasing the limit for when electricity prices become too high for hydrogen production. Figure 2 shows an example of the impact on the revenue of a hydrogen plant connected to a DH system. District heating welcomes heat from Power-to-X The heat from PtX is well suited for integration into a carbon- neutral DH system. It could be a valuable green heat source with high temperatures, large volumes, and a high number of operating hours. This is why all the central DH systems in Den- mark are investigating the possibilities for connecting to future PtX facilities. It is expected that all strategic energy plans and heat plans in these areas will discuss integration of PtX and DH. A DH system will have several heat sources, and the value of the heat for PtX will depend on the other heat sources in the system. In the summer, heat is abundant and cheap, so the hydrogen plant will experience lower prices than during winter peak load. Other types of heat production may also depend on the electricity price. This means that the revenue of the surplus heat will vary hour-by-hour and season-by-season — some- thing to include in the business case considerations. Integrating heat and hydrogen benefits other sectors PtX heat for DH promotes integration across sectors such as power, heating, transport, waste, industry, and agriculture. The results of this are increased energy efficiency, lower costs, and new possibilities.

Direct electrification is one option, but if available, DH is often a competitive alternative. Figure 3 illustrates how waste heat from PtX can substitute fossil-based heat used in the industry if the heating infrastructure is or becomes available. This type of synergies is already known and used in Denmark, where WtE plants and DH systems are closely coupled and shows the power and potential of sector integration.

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THE RECOMMENDATIONS IN THE REPORT ARE GROUPED INTO FOUR TOPICS • The value of integrating DH and PtX is overlooked • Investments in energy infrastructure are needed • Development and demonstration – including a list of what is needed • Planning, timing, and framework conditions}

An example of this is the challenges faced by industrial sites needing to convert from fossil-based to green process heat.

For further information please contact: Hanne Kortegaard Støchkel,

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